Fuel cell systems using solid polymer membrane electrolytes are known in the prior art. It is desirable in such fuel cells to maintain the electrolyte membrane in a moist condition for most efficient operation of the cells. U. S. Pat. No. 3,061,658 to Blackmer discloses a fuel cell construction which uses a solid polymer electrolyte membrane and which humidifies the oxygen reactant stream to introduce water into the cell to moisten the membrane. This approach can cause problems because the product water formed by the electrolytic reaction appears on the cathode surface of the membrane, as does water which is transferred from the anode side to the cathode side by proton flux. If the cathode side is too moist, a water sheet forming thereon will block access to the cathode by the oxygen reactant. A better approach to solving this problem of membrane dryout is to provide moisture to the anode side of the cell.